Bone anchor assembly with twist-in-place pressure insert

ABSTRACT

A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver member or head, a retaining and articulating structure, and a pressure insert disposed between the shank upper portion and a rod. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod and a receiver cavity. The retaining and articulating structure attaches to the shank and rotates with the shank in the cavity during positioning. The pressure insert presses upon the shank upper portion and not the retaining and articulating structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/802,668 filed Jun. 11, 2010, which is a continuation of U.S.application Ser. No. 11/140,343 filed May 27, 2005, all of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery, and particularly to insertsfor such screws.

Bone screws are utilized in many types of spinal surgery, such as forosteosynthesis, in order to secure various implants to vertebrae alongthe spinal column for the purpose of stabilizing and/or adjusting spinalalignment. Although both closed-ended and open-ended bone screws areknown, open-ended screws are particularly well suited for connections torods and connector arms, because such rods or arms do not need to bepassed through a closed bore, but rather can be laid or urged into anopen channel within a receiver or head of such a screw.

Typical open-ended bone screws include a threaded shank with a pair ofparallel projecting branches or arms which form a yoke with a U-shapedslot or channel to receive a rod. Hooks and other types of connectors,as are used in spinal fixation techniques, may also include open endsfor receiving rods or portions of other structure.

A common mechanism for providing vertebral support is to implant bonescrews into certain bones which then in turn support a longitudinalstructure such as a rod, or are supported by such a rod. Bone screws ofthis type may have a fixed head or receiver relative to a shank thereof.In the fixed bone screws, the rod receiver head cannot be moved relativeto the shank and the rod must be favorably positioned in order for it tobe placed within the receiver head. This is sometimes very difficult orimpossible to do. Therefore, polyaxial bone screws are commonlypreferred.

Open-ended polyaxial bone screws allow rotation of the head or receiverabout the shank until a desired rotational position of the head isachieved relative to the shank. Thereafter, a rod can be inserted intothe head or receiver and eventually the head is locked or fixed in aparticular position relative to the shank. However, in certaininstances, a surgeon may desire to set and fix the angular position ofthe head or receiver relative to the shank independently of rodinsertion or rod locking. Additionally, it may be desirable to reset andfix the angle of orientation of the head or receiver during the surgicalprocedure.

SUMMARY OF THE INVENTION

A polyaxial bone screw assembly according to the invention includes ashank having an upper portion and a body for fixation to a bone; a heador receiver defining an open channel; and at least one compression orpressure insert. The shank is connected to the head or receiver at theupper portion and the shank body is swivelable with respect to the heador receiver. The pressure insert is receivable in the head open channel.The pressure insert includes a base and a head engagement structure. Thepressure insert base is frictionally engageable with the shank upperportion and the head engagement structure is engageable with thereceiver head. The pressure insert has an articulation position whereinthe insert head engagement structure is engaged with the head and thebase frictionally engages a projecting end of the shank upper portionwith the pressure insert exerting an independent force or pressure onthe shank upper portion sufficient to retain the shank body in aselected angle with respect to the head without continuously appliedcompression by a closure top through the rod.

Pressure inserts according to the invention include a side loadinginsert having a ratcheted outer surface for engagement with a ratchetedinner surface on the bone screw receiver head. Another embodimentincludes a cam insert, side loaded or down loaded into the bone screwreceiver head, having sloped upper surfaces for engagement with an uppershoulder of a recess formed in the bone screw receiver head.

Objects and Advantages of the Invention

Therefore, objects of the present invention include: providing animproved spinal implant assembly for implantation into vertebrae of apatient; providing such an assembly that includes an open-headedimplant, a shank pivotally connected to the implant head, a rod or otherstructural element, and a pressure insert disposed between the shank andthe rod; providing a pressure insert that may be utilized independentlyto set an angle of articulation of the shank with respect to the headprior to or after insertion of the rod; providing such an assembly thathas a low profile after final installation; providing such an assemblyin which the pressure insert may be assembled into a bone screw headprior or subsequent to installing the bone screw into bone; providingsuch an assembly in which the bone screw includes a retaining structurethat includes a non-slip feature for driving the shank into bone; andproviding such an assembly that is easy to use, especially adapted forthe intended use thereof and wherein the implant assembly components arecomparatively inexpensive to produce.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an assembly according to theinvention including a shank with a capture structure at one end thereof,a head or receiver, a retaining and articulating structure and aside-loading pressure insert.

FIG. 2 is a perspective view of the assembly of FIG. 1 shown assembled.

FIG. 3 is an enlarged, perspective view of the insert of FIG. 1.

FIG. 4 is a front elevational view of the insert of FIG. 3.

FIG. 5 is a side elevational view of the insert of FIG. 3.

FIG. 6 is a top plan view of the insert of FIG. 3.

FIG. 7 is a bottom plan view of the insert of FIG. 3.

FIG. 8 is a cross-sectional view of the insert taken along the line 8-8of FIG. 6.

FIG. 9 is an enlarged and partial front elevational view of theassembled shank, bone screw head and retaining and articulatingstructure of FIG. 2 shown prior to insertion of the side-loading insert.

FIG. 10 is an enlarged and partial front elevational view of theassembly of FIG. 2.

FIG. 11 is an enlarged and partial side elevational view of the assemblyof FIG. 2 shown with the side-loading insert in engagement with the bonescrew shank, setting the shank in an angle of articulation with respectto the head.

FIG. 12 is a partial front elevational view of a bone screw driving toolaccording to the invention.

FIG. 13 is a partial side elevational view of the bone screw drivingtool of FIG. 12.

FIG. 14 is an enlarged and partial cross-sectional view of the head andinsert taken along the line 14-14 of FIG. 2, shown with the shank andretaining and articulating structure in front elevation and furthershown with the driving tool of FIG. 12.

FIG. 15 is a cross-sectional view taken along the line 15-15 of FIG. 14.

FIG. 16 is an enlarged and partial cross-sectional view of the head,retaining and articulating structure and insert taken along the line16-16 of FIG. 2, shown with the shank in front elevation and furthershown with the driving tool of FIG. 12 shown in the side elevationalview of FIG. 13.

FIG. 17 is a reduced view of the bone screw and driving tool of FIG. 14further shown in exploded view with a guide wire and vertebra.

FIG. 18 is an enlarged view of the bone screw, driving tool, guide wireand vertebra of FIG. 17 shown in cooperation during a process of bonescrew installation.

FIG. 19 is an exploded perspective view of a nested bone screw fastenerassembly including a fastener base integral with a break-off head and aninner set screw.

FIG. 20 is an enlarged cross-sectional view taken along the line 20-20of FIG. 19 and shown with a set screw tool.

FIG. 21 is a cross-sectional view similar to FIG. 20, showing the setscrew inserted in the fastener base.

FIG. 22 is a partial cross-sectional view of the bone screw and insertassembly of FIG. 14 shown with a rod, also in cross-section and in aprocess of mating with the nested bone screw fastener assembly of FIG.21.

FIG. 23 is a partial cross-sectional view, similar to FIG. 22 shown witha manipulation tool in a process of moving the side-loaded insertupwardly and away from the bone screw shank to allow for pivoting of thebone screw shank with respect to the head.

FIG. 24 is a partial cross-sectional view, similar to FIGS. 22 and 23,shown with the shank fixed at a selected angle with respect to the headby frictional contact with the insert prior to frictional contactbetween the rod and the nested fastener assembly.

FIG. 25 is a reduced partial and cross-sectional view similar to FIG.24, showing the break-off head of the nested closure assembly beingremoved with a torquing tool.

FIG. 26 is a partial cross-sectional view similar to FIG. 25 shown witha set screw tool engaged with the inner set screw in a process oftightening the set screw against the rod.

FIG. 27 is a cross-sectional view similar to FIG. 26 showing a fullyinstalled nested fastener in front elevation.

FIG. 28 is a partial cross-sectional view similar to FIG. 26, showingengagement and removal of the nested fastener from the bone screw headwith a set screw tool.

FIG. 29 is an exploded perspective view of a second embodiment of anassembly according to the invention including a shank with a capturestructure at one end thereof, a head, a retaining and articulatingstructure and an insert.

FIG. 30 is an enlarged cross-sectional view of the bone screw head andretaining and articulating structure taken along the line 30-30 of FIG.29, shown with the retaining and articulating structure turned on a sidethereof for insertion into the head.

FIG. 31 is a cross-sectional view similar to FIG. 30 showing theretaining and articulating structure turned back into the orientationshown in FIG. 29 but within the head in preparation for engagement withthe capture structure of the shank.

FIG. 32 is an enlarged front elevational view of the insert of FIG. 29.

FIG. 33 is an enlarged side elevational view of the insert of FIG. 29.

FIG. 34 is an enlarged top plan view of the insert of FIG. 29.

FIG. 35 is an enlarged bottom plan view of the insert of FIG. 29.

FIG. 36 is an enlarged partial cross-sectional view of the head similarto FIG. 31 showing the shank and capture structure in front elevation ina process of engagement with the retaining and articulating structure,also shown in front elevation.

FIG. 37 is a partial cross-sectional view of the head similar to FIG. 36showing the shank capture structure engaged with the retaining andarticulating structure and showing a process of insertion of the insertinto the head.

FIG. 38 is a cross-sectional view taken along the line 38-38 of FIG. 37.

FIG. 39 is a cross-sectional view taken along the line 39-39 of FIG. 37.

FIG. 40 is a reduced partial cross-sectional view of the head and frontelevational view of the shank, retaining and articulating structure andinsert similar to FIG. 37, showing the insert rotated to a shank settingposition and the assembly in a process of being driven into bone with adriving tool.

FIG. 41 is an enlarged cross-sectional view taken along the line 41-41of FIG. 40.

FIG. 42 is an enlarged and partial cross-sectional view of the headsimilar to FIG. 40, shown with the shank, retaining and articulatingstructure and insert in front elevation and further showing a rod incross-section and an engaged closure top in front elevation.

FIG. 43 is an exploded perspective view of a third embodiment of anassembly according to the invention including a shank with a capturestructure at one end thereof, a head, a retaining and articulatingstructure and an insert.

FIG. 44 is an enlarged cross-sectional view of the bone screw head andretaining and articulating structure taken along the line 44-44 of FIG.43, shown with the retaining and articulating structure turned on a sidethereof for insertion into the head.

FIG. 45 is a cross-sectional view similar to FIG. 44 showing theretaining and articulating structure turned back into the orientationshown in FIG. 43 but within the head in preparation for engagement withthe capture structure of the shank.

FIG. 46 is a partial cross-sectional view of the head similar to FIG. 45showing the shank and capture structure in front elevation in a processof engagement with the retaining and articulating structure, also shownin front elevation.

FIG. 47 is a partial cross-sectional view of the head similar to FIG. 46showing the shank capture structure engaged with the retaining andarticulating structure and showing a process of insertion of the insertinto the head.

FIG. 48 is a cross-sectional view taken along the line 48-48 of FIG. 47.

FIG. 49 is a cross-sectional view taken along the line 49-49 of FIG. 47.

FIG. 50 is an enlarged front elevational view of the insert of FIG. 43.

FIG. 51 is an enlarged side elevational view of the insert of FIG. 43.

FIG. 52 is a reduced partial cross-sectional view of the head and frontelevational view of the shank, retaining and articulating structure andinsert similar to FIG. 47, showing the insert rotated to a shank settingposition and the assembly in a process of being driven into bone with adriving tool.

FIG. 53 is an enlarged cross-sectional view taken along the line 53-53of FIG. 52.

FIG. 54 an enlarged and partial cross-sectional view of the head similarto FIG. 52, shown with the shank, retaining and articulating structureand insert in front elevation and further showing a rod in cross-sectionand an engaged closure top in front elevation.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

With reference to FIGS. 1-28, the reference numeral 1 generallydesignates a polyaxial bone screw assembly according to the presentinvention. The assembly 1 includes a shank 4 that further includes abody 6 integral with an upwardly extending capture structure 8; a heador receiver 10; a retaining and articulating structure or ring 12; and aside-loading pressure insert 14. The shank 4, head or receiver 10,retaining and articulating structure 12 and insert 14 are preferablyassembled prior to implantation of the shank body 6 into a vertebra 15,which procedure is shown in FIGS. 17 and 18.

FIGS. 19-28 further show a closure structure or nested fastener,generally 18, of the invention for capturing a longitudinal member suchas a rod 21 within the head or receiver 10. The insert 14 allows forsetting an angle of articulation between the shank body 6 and the heador receiver 10 prior to insertion of the rod 21, if desired. Uponinstallation, which will be described in detail below, the nestedfastener 18 presses against the rod 21 that in turn presses against theinsert 14 that presses against the capture structure 8 which biases theretaining and articulating structure 12 into fixed frictional contactwith the head or receiver 10, so as to fix the rod 21 relative to thevertebra 15. The head or receiver 10 and shank 4 cooperate in such amanner that the head 10 and shank 4 can be secured at any of a pluralityof angles, articulations or rotational alignments relative to oneanother and within a selected range of angles both from side to side andfrom front to rear, to enable flexible or articulated engagement of thehead 10 with the shank 4 until both are locked or fixed relative to eachother.

The shank 4, best illustrated in FIGS. 1 and 2, is elongate, with theshank body 6 having a helically wound bone implantable thread 24extending from near a neck 26 located adjacent to the capture structure8 to a tip 28 of the body 6 and extending radially outward therefrom.During use, the body 6 utilizing the thread 24 for gripping andadvancement is implanted into the vertebra 15 leading with the tip 28and driven down into the vertebra 15 with an installation or drivingtool 31 so as to be implanted in the vertebra 15 to near the neck 26, asshown in FIG. 24, and as is described more fully in the paragraphsbelow. The shank 4 has an elongate axis of rotation generally identifiedby the reference letter A. It is noted that any reference to the wordstop, bottom, up and down, and the like, in this application refers tothe alignment shown in the various drawings, as well as the normalconnotations applied to such devices, and is not intended to restrictpositioning of the assembly 1 in actual use.

The neck 26 extends axially outward and upward from the shank body 6.The neck 26 may be of reduced radius as compared to an adjacent top 32of the body 6. Further extending axially and outwardly from the neck 26is the capture structure 8 that provides a connective or capturestructure disposed at a distance from the body top 32 and thus at adistance from the vertebra 15 when the body 6 is implanted in thevertebra 15.

The capture structure 8 is configured for connecting the shank 4 to thehead or receiver 10 and capturing the shank 4 in the head 10. Thecapture structure 8 has an outer substantially cylindrical surface 34having a helically wound guide and advancement structure thereon whichin the illustrated embodiment is a V-shaped thread 36 extending fromnear the neck 26 to adjacent to an annular upper surface 38. Although asimple thread 36 is shown in the drawings, it is foreseen that otherstructures including other types of threads, such as buttress andreverse angle threads, and non threads, such as helically wound flangeswith interlocking surfaces, may be alternatively used in alternativeembodiments of the present invention.

Projecting along the axis A upwardly and outwardly from the annularsurface 38 of the capture structure 8 is a curved or dome-shaped top 42.The illustrated top 42 is radially extending, convex, substantiallyhemispherical or dome-shaped, preferably having a substantially uniformradius of generation to provide for positive engagement with the insert14 at almost any orientation of the shank 4, as will be described morefully below. It is foreseen that in certain embodiments the radius mayvary depending upon the needs and desires of the particular structureand the domed top 42 may have a shape that is only partly spherical orsome other shape. For example, the domed top could be radiused at thelocation of greatest projection along the axis A and otherwise featheredalong a periphery thereof so as to not have a continuous uniform radiusof generation throughout but rather a continually changing radius ofgeneration along at least the length thereof.

The shank 4 shown in some of the drawings is cannulated, having a smallcentral bore 44 extending an entire length of the shank 4 along the axisA. The bore 44 has a first circular opening 46 at the shank tip 28 and asecond circular opening 48 at the top surface 42. The bore 44 is coaxialwith the threaded body 6 and the capture structure outer surface 34. Thebore 44 provides a passage through the shank 4 interior for a length ofwire or pin 49 as shown in FIGS. 17 and 18, inserted into the vertebra15 prior to the insertion of the shank body 6, the pin 49 providing aguide for insertion of the shank body 6 into the vertebra 15.

Referring to FIGS. 1, 2, 9-11 and 14, the head or receiver 10 has agenerally cylindrical outer profile with a substantially cylindricalbase 50 integral with a pair of opposed upstanding arms 52 that extendfrom the base 50 to a top surface 54. The arms 52 form a U-shaped cradleand define a U-shaped channel 56 between the arms 52 and include anupper opening 57 and a lower seat 58 having substantially the sameradius as the rod 21 for operably snugly receiving the rod 21.

Each of the arms 52 has an interior surface 60 that defines the innercylindrical profile and includes a partial helically wound guide andadvancement structure 62. In the illustrated embodiment, the guide andadvancement structure 62 is a partial helically wound flangeformconfigured to mate under rotation with a similar structure on the nestedfastener 18, as described more fully below. However, it is foreseen thatthe guide and advancement structure 62 could alternatively be a V-shapedthread, a buttress thread, a square thread, a reverse angle thread orother thread like or non-thread like helically wound advancementstructures for operably guiding under rotation and advancing thefastener 18 downward between the arms 52.

Tool engaging grooves 64 are formed on outer substantially cylindricalsurfaces 65 of the arms 52 which may be used for holding the head 10during assembly with the shank 4 and the retaining and articulatingstructure 12 and also during the implantation of the shank body 6 intovertebra 15. The illustrated grooves 64 are disposed near the top 54 ofthe head 10 and each extend partially circumferentially about aperiphery of each arm 52 and may include an undercut or dovetail featurefor engagement with a holding tool. A holding tool (not shown) isequipped with structure sized and shaped to be received in the grooves64. The holding tool and respective grooves 64 may be configured foreither a twist on/twist off engagement with the head, or a flexible snapon/snap off engagement wherein the holding tool has legs which splayoutwardly to position the tool for engagement in the grooves 64 or acombination thereof. It is foreseen that the grooves 64 and thecooperating holding tool may be configured to be of a variety of sizesand locations along the cylindrical surfaces 65. Also disposed centrallyon each arm 52 is an oval through-bore 68 that allows for manipulationof the insert 14 as will be described more fully below.

Communicating with the U-shaped channel 56 and located within the base50 of the head or receiver 10 is a chamber or cavity 78 substantiallydefined by an inner surface 80 of the base 50, the cavity 78 openingupwardly into the U-shaped channel 56. The inner surface 80 issubstantially spherical, with at least a portion thereof forming apartial internal spherical seating surface 82 having a first radius. Thesurface 82 is sized and shaped for mating with the retaining andarticulating structure 12, as described more fully below.

The base 50 further includes a restrictive neck 83 defining a bore 84communicating with the cavity 78 and a lower exterior 86 of the base 50.The bore 84 is coaxially aligned with respect to a rotational axis B ofthe head 10. The bore 84 may be conically counterbored or beveled in aregion 85 to widen the angular range of the shank 4.

The neck 83 and associated bore 84 are sized and shaped to be smallerthan a radial dimension of the retaining and articulating structure 12,as will be discussed further below, so as to form a restriction at thelocation of the neck 83 relative to the retaining and articulatingstructure 12, to prevent the retaining and articulating structure 12from passing from the cavity 78 and out into the lower exterior 86 ofthe head 10 when the retaining and articulating structure 12 is seated.However, it is foreseen that the retaining and articulating structurecould be compressible (such as where such structure has a missingsection) and that the retaining structure could be loaded up through theneck 83 and then allowed to expand and fully seat in the sphericalseating surface.

It is foreseen that the inner surface 80 may further include an elongateupper loading recess (not shown) for accommodating and loading theretaining and articulating structure 12 into the cavity 78. Such aloading recess would be generally vertically disposed in the head 10,extending between and communicating with both the channel 56 and thecavity 78, allowing for ease in top loading the retaining andarticulating structure 12 into the cavity through the upper opening 57and otherwise allowing for the spherical wall 80 of the head 10 to havea radius allowing for substantial thickness and strength of the headbase 50.

On each arm 52, disposed adjacent to and directly below the guide andadvancement structure 62 is an inner, inset surface 87 having a width ordiameter greater than a distance between the interior surfaces 60 of thearms 52. An inner insert receiving surface 88 is located between thesurface 87 and the inner substantially spherical surface 80. The insertreceiving surface 88 includes a band of ridges or teeth 89 extendingacross each arm 52 and running parallel to the head top surface 54. Theridges or teeth 89 each incline in a downward direction toward the base50 and are sized and shaped to cooperate with ratchet teeth disposed onthe insert 14 as will be described more fully below. The inner surface87 provides space for insertion of the insert 14 into the head 10 withno initial engagement of the teeth 89 with the head 10 as illustrated inFIG. 10.

The retaining and articulating structure or ring 12 is used to retainthe capture structure 8 of the shank 4 within the head 10. The retainingand articulating structure 12, best illustrated by FIGS. 1, 14, 16 and18, has an operational central axis that is the same as the elongateaxis A associated with the shank 4, but when the retaining andarticulating structure 12 is separated from the shank 4, the axis ofrotation is identified as an axis C. The retaining and articulatingstructure 12 has a central bore 90 that passes entirely through theretaining and articulating structure 12 from a top surface 92 to abottom surface 94 thereof. A first inner cylindrical surface 96 definesa substantial portion of the bore 90, the surface 96 having a helicallywound guide and advancement structure thereon as shown by a helical ribor thread 98 extending from adjacent the top surface 92 to adjacent thebottom surface 94. Although a simple helical rib 98 is shown in thedrawings, it is foreseen that other helical structures including othertypes of threads, such as buttress and reverse angle threads, and nonthreads, such as helically wound flanges with interlocking surfaces, maybe alternatively used in an alternative embodiment of the presentinvention. The inner cylindrical surface 96 with helical rib 98 areconfigured to mate under rotation with the capture structure outersurface 34 and helical advancement structure or thread 36, as describedmore fully below.

The retaining and articulating structure 12 has a radially outerpartially spherically shaped surface 104 sized and shaped to mate withthe partial spherically shaped seating surface 82 of the head and havinga radius approximately equal to the radius associated with the surface82. The retaining and articulating structure radius is larger than theradius of the neck 83 of the head 10. Although not required, it isforeseen that the outer partially spherically shaped surfaced 104 may bea high friction surface such as a knurled surface or the like.

The retaining and articulating structure top surface 92 extends from thecentral bore 90 to the outer surface 104. The top surface 92 is disposedat an angle with respect to the bottom surface 94, with the top surface92 sloping in a downward direction toward the bottom surface 94 as thetop surface 92 extends toward the outer surface 104. As illustrated inFIG. 11 and discussed more fully below, the angle of inclination of thetop surface 92 is configured for contact and frictional engagement witha bottom surface of the insert 14.

The retaining and articulating structure 12 further includes a toolengagement structure in the form of a transverse slot 106 formed in thetop surface 92 for engagement with the driving tool 31 shown in FIGS. 17and 18. As will be described more fully below, the tool 31 is configuredto fit within the transverse slot 106 on either side of the domed top 42of the shank 4 and utilized for driving the shank body 6 into thevertebra 15.

The elongate rod or longitudinal member 21 that is utilized with theassembly 1 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a smooth, outer cylindrical surface 108 of uniformdiameter. The rod 21 is preferably sized and shaped to snugly seat nearthe bottom of the U-shaped channel 56 of the head 10 and, during normaloperation, is positioned slightly above the bottom of the channel 56 atthe lower seat 58. In the illustrated embodiment, the domed top 42 ofthe shank 4 does not come into direct contact with the rod 21, butrather, the side-loading insert 44 is received within the bone screwhead 10 prior to rod insertion, and ultimately is positioned between therod 21 and the top 42.

The insert 14 is best illustrated in FIGS. 3-7. The insert 14 includes abase 110 integral with a pair of upstanding arms 112. The base 110 andarms 112 form a generally U-shaped, open, through-channel 114 having asubstantially cylindrical bottom seating surface 116 configured tooperably snugly engage the rod 21. Each arm 112 has a faceted outerprofile with a lower facet or face 120 extending from the base 110 andintegral with a side facet or face 122 that includes a bar or rack ofinclined teeth 124 for ratcheting the insert 14 down by degrees into thehead 10 in cooperation with the ridges or teeth 89 disposed on theinsert receiving surface 88, as will be described more fully below. Eachside facet or face 122 extends between one of the lower facets 120 and atop surface 126. The ratchet teeth 124 are disposed near the top surface126 and each tooth 124 runs in a direction parallel to the top surface126. Furthermore, each tooth 124 includes a surface 130 inclined in anoutward and upward direction toward the top surface 126. The teeth 124are thus readily movable or ratcheted downwardly toward the cavity 78 ofthe bone screw head 10 when desired, after side insertion of the insert14 into the head 10 as illustrated in FIGS. 1 and 2. Once the teeth 124are pressed downwardly into engagement with the teeth 89, the insert 14resists upward movement toward the opening 57 of the bone screw headchannel 56.

Disposed on either side of each side facet 122 are lateral facets 128that terminate at planar outer edge surfaces 132. Also extending betweenthe edge surfaces 132 and the base 110 are lower facets 134. A pair ofopposing, squared-off notches 136 are formed on each lower facet 134 ina central location where the facet 134 contacts the edge surfaces 132.The notches 136 are sized and shaped to correspond and cooperate withthe transverse slot 106 of the retaining and articulating structure 12to allow for insertion of the driving tool 31 through the notches 136and into the slot 106 for engagement with the retaining and articulatingstructure during installation of the shank body 6 into bone.

Disposed centrally on a bottom surface 138 of the base 110, opposite theseating surface 116 is a concave, substantially spherical formation 140.A cannulation bore 142 extends through a central portion of theformation 140. The formation 140 is sized and shaped to snuglyfrictionally fit about the domed top 42 of the capture structure 8. Aswill be described in greater detail below, as the insert 14 is ratcheteddownwardly into contact with the domed top 42 and the retaining andarticulating structure 12, the insert 14 may be used to set thearticulation of the shank body 6 with respect to the bone screw head 10prior to insertion and locking of the rod 21 into the head 10, or byinserting and compressing the rod 21 with the closure top 18 and thenreleasing the closure top 18. As illustrated in FIG. 23 and discussedmore fully below, the side bores or apertures 68 formed in the head 10allow for manipulation of the insert 14 with respect to the dome shapedtop 42 by a tool 146 that has opposed pinchers or prongs 147 forextending through the bores 68 and pressing against the arms 112 of theinsert 14 to loosen the insert 14 from the head 10. Eventually, the rod21 is placed in the U-shaped channel 56 and/or the rod 21 which has beenplaced in the channel directly, abutingly engages or re-engages theinsert 14 that in turn engages the shank capture structure domed top 42,as shown, for example, in FIGS. 11 and 22, consequently biasing theshank 4 downwardly in a direction toward the base 50 of the head 10 whenthe assembly 1 is fully assembled. The shank 4 and retaining andarticulating structure 12 are thereby locked in position relative to thehead 10 by the rod 21 firmly pushing downward on the insert 14 and theshank domed top surface 42.

With reference to FIGS. 12-18, the driving tool 31 according to theinvention includes a handle 150, an elongate cylindrical stem or shaft154 and an engagement structure 156. The engagement structure 156 isconfigured to operably mate with both the insert 14 and the retainingand articulating structure 12 at the transverse slot 106 thereof. Theshaft 154 with attached engagement structure 156 is receivable in andpasses through the interior of the bone screw head 10. The stem or shaft154 is rigidly attached to the handle 150 and coaxial therewith. Thehandle 150 includes outer grooves 158 disposed about an outercylindrical surface 160 thereof to aid in gripping and rotating therespective components.

The engagement structure 156 includes an oblong support 162 with twoopposed arms 164 extending downwardly from the support 162 and away fromthe shaft 154 at either end of the support 162. The oblong support 162has a substantially cylindrical lower surface 166 sized and shaped tofit within the U-shaped channel 114 of the insert 14 and operably matewith the bottom seating surface 116 during turning rotation and drivingthe of the bone screw shank 4 into bone. Each arm 164 further includesan extension 168 sized and shaped to fit within the transverse slot 106of the retaining and articulating structure 12. As illustrated in FIG.16, each extension 168 has a thickness such that the extension 168 fitssnugly between the threaded cylindrical surface 34 of the capturestructure 8 and the inner surface 80 of the head 10, while a bottomsurface 170 of the extension 168 seats evenly on a base surface 171 ofthe transverse slot 106. Each arm 164 also includes an inner seatingsurface 174 disposed parallel to the base surface 171. Each innerseating surface 174 is sized and shape to seat upon and engage theannular top surface 38 of the capture structure 8 when the extensions168 are seated within the transverse slot 106. Thus, the engagementstructure 156 of the driving tool 31 engages the bone screw assembly 1at the lower cylindrical surface 166, the extensions 168 and the innerseating surface 174 when driving the shank body 6 into the vertebra 15,as will be described more fully below. The driving tool 31 also includesa centrally located cannulation bore 176 extending along a lengththereof, sized shaped and located to cooperate with the cannulation bore44 of the bone screw shank 4 and the cannulation bore 142 of the insert14.

With particular reference to FIGS. 19-21, the closure structure ornested fastener 18 can be any of a variety of different types of closurestructures for use in conjunction with the present invention withsuitable mating structure on the upstanding arms 52 of the head 10. Thefastener 18 screws between the spaced arms 52. The illustrated fastener18 includes an outer fastener 204 and an uploaded set screw 206. Thefastener 204 includes a base 208 integral or otherwise attached to abreak-off head 210. The base 208 cooperates with the head 10 of the bonescrew assembly 1, as illustrated in FIGS. 22-28, to close the headU-shaped channel 56 and to clamp the spinal fixation rod 21 within thebone screw head 10. The break-off installation head 210 includes afaceted outer surface 220 sized and shaped for engagement with a tool221 for installing the fastener 204 to the bone screw head or receiver10 and thereafter separating the break-off head 210 from a respectivebase 208 when installation torque exceeds selected levels.

The base 208 of the fastener 204 is substantially cylindrical, having anaxis of rotation D and an external surface 250 having a guide andadvancement structure 252 disposed thereon. The guide and advancementstructure 252 is matingly attachable to the guide and advancementstructure 62 of the bone screw head 10. As with the guide andadvancement structure 62, the guide and advancement structure 252 can beof any type, including V-type threads, buttress threads, reverse anglethreads, or square threads. Preferably the guide and advancementstructure 252 is a helically wound flange form that interlocks with thereciprocal flange form as part of the guide and advancement structure 62on the interior of the bone screw arms 52. The guide and advancementstructures 62 and 252 are preferably of a type that do not exertradially outward forces on the arms 52 and thereby avoid tendenciestoward splaying of the arms 52 of the bone screw head 10, when thefastener 204 is tightly torqued into the head 10.

The fastener 204 includes an internal, centrally located through-bore254. At the base 208, the bore 254 is substantially defined by a guideand advancement structure, shown in FIGS. 20 and 21 as an internalV-shaped thread 256. The thread 256 is sized and shaped to receive thethreaded set screw 206 therein as will be discussed in more detailbelow. Although a traditional V-shaped thread 256 is shown, it isforeseen that other types of helical guide and advancement structuresmay be used. Near a substantially annular planar top surface 258 of thebase 208, an abutment shoulder 260, extends uniformly radially inwardly.The abutment shoulder 260 is spaced from the V-shaped thread 256 andsized and shaped to be a stop for the set screw 206, prohibiting the setscrew 206 from advancing out of the top 258 of the base 208. It isforeseen that alternatively, the set screw 206 may be equipped with anoutwardly extending abutment feature near a base thereof, withcomplimentary alterations made in the base 208, such that the set screw206 would be prohibited from advancing out of the top 258 of the base208 due to abutment of such outwardly extending feature against asurface of the base 208.

An inner cylindrical wall 262 separates the abutment shoulder 260 fromthe thread 256. The cylindrical wall 262 has a diameter slightly greaterthan a root or major diameter of the internal thread 256. The wall 262partially defines a cylindrical space or passage 264 for axialadjustable placement of the screw 206 with respect to the rod 21 as willbe discussed in more detail below.

The fastener 204 further includes the break-off head 210 that isintegral or otherwise attached to the fastener 204 at a neck or weakenedregion 266. The neck 266 is dimensioned in thickness to control thetorque at which the break-off head 210 separates from the fastener 204.The preselected separation torque of the neck 266 is designed to providesecure clamping of the rod 21 by the fastener 204 before the head 210separates. For example, 120 inch pounds of force may be a selectedbreak-off torque. The illustrated, hexagonal faceted surfaces 220 of thebreak-off head 210 enables positive, non-slip engagement of the head 210by the installation and torquing tool 221 illustrated in FIG. 25.Separation of the break-off head 210 leaves only the more compact base208 of the fastener 204 installed in the bone screw head or receiver 10,so that the installed fastener 204 has a low profile.

The base 208 of the fastener 204 may include structure to provideclamping engagement between the base 208 and the rod 21. In theembodiment disclosed in FIGS. 19-28, a bottom surface 268 of the base208 has an interference structure in the form of a “cup point” orV-shaped ridge or ring 270. The V-ring 270 operably cuts into the outersurface 108 of the rod 21 during assembly, when the fastener 204 isthreaded into the screw head 10, so that the fastener more positivelysecures the rod 21 against rotational and translational movement of therod 21 relative to the bone screw head 10. As the rod 21 may be bent orskewed with respect to the head 10 at a location of engagement betweenthe rod 21 and the fastener 204, only a portion or a side of the V-ring270 may engage with and cut into the rod 21. It is also foreseen that insome embodiments, clamp enhancing structure on the fastener 204, such asthe V-ring 270, or surface finish such as knurling, may or may not benecessary or desirable.

The uploadable set screw 206 has a substantially planar top 276 and abottom 277. The set screw 206 is substantially cylindrical in shape,having an axis of rotation E, and includes an outer cylindrical surface278 with a V-shaped thread 280 extending from the top 276 to the bottom277 thereof. The surface 278 and thread 280 are sized and shaped to bereceived by and mated with the inner thread 256 of the fastener base 208in a nested relationship. Thus, in operation, the axis of rotation E isthe same as the axis of rotation D of the fastener 204.

The embodiment of the set screw 206 best illustrated in FIGS. 19-21includes interference structure for enhancing clamping or settingengagement with the surface 108 of the rod 21. The bottom 277 of theillustrated set screw 206 has a centrally located set point 282 and aperipherally located cup point or V-shaped set ring 284 projectingtherefrom. The set point 282 and the set ring 284 are designed to cutinto the surface 108 of the rod 21 when the set screw 206 is tightlyfastened into the fastener base 208. The set point 282 projectsoutwardly from the bottom 277 to a location beyond the outermost surfaceof the set ring 284. Thus, the set point 282 is an initial and primarysource of engagement with the rod 21, directly pressing against the rod18 along the central axis of rotation D of the set screw 206. As withthe V-ring 270 of the fastener 204, the V-ring 284 may contact and pressagainst the rod 21 only along a portion thereof if the rod 21 is bent orotherwise disposed in a skewed relationship with the bone screw head 10.It is foreseen that a domed shape projection (not shown) may be utilizedin lieu of the set point 282. Such a projection may be a radiallyextending convex, curved, partially spherical or dome-shapedinterference or compressive structure, having a substantially uniformradius to provide for positive engagement with the rod 21 at the surface108. Such a domed structure may extend a greatest distance along thecentral axis E. It is also foreseen that other structures for enhancingclamping, such as knurling or the like may be used in some embodimentsor none in others.

The set screw 206 includes a central aperture 286 formed in the top 276and defined by faceted side walls 288 and a hexagonal bottom seatingsurface 289, forming a hex-shaped internal drive for positive, non-slipengagement by a set screw installment and removal tool such as anAllen-type wrench 290 as depicted in FIGS. 20, 26 and 28. With referenceto FIG. 20, the central aperture 286 cooperates with the centralinternal bore 254 of the fastener 204 for accessing and uploading theset screw 206 into the fastener 204 prior to engagement with the bonescrew head 10. After the nested fastener 18 engages the bone screw head10, and the break-off head 210 is broken off, the tool 290 is used toset and lock the set screw 206 against the rod 21 as illustrated in FIG.26.

There are circumstances under which it is desirable or necessary torelease the rod 21 from the bone screw head 10. For example, it might benecessary for a surgeon to re-adjust components of a spinal fixationsystem, including the rod 21, during an implant procedure, following aninjury to a person with such a system implanted. In such circumstances,the tool 290 may be used to remove both the set screw 206 and attachedfastener base 208 as a single unit, with the set screw 206 contactingand contained within the base 208 by the abutment shoulder 260. Thus, asillustrated in FIG. 28, rotation of the tool 290 engaged with the setscrew 206 backs both the set screw 206 and the fastener base 208 out ofthe guide and advancement structure 252 in the arms 52 of the bone screwhead 10, thereby releasing the rod 21 for removal from the bone screwhead 10 or repositioning of the rod 21. It is foreseen that otherremoval structures such as side slots or other screw receiving andengagement structures may be used to engage the set screw 206 that isnested in the fastener base 208.

With reference to FIGS. 1 and 2, prior to the polyaxial bone screwassembly 1 being implanted in the vertebra 15, the retaining andarticulating structure 12 is typically first inserted or top-loaded,into the head U-shaped channel 56, and then into the cavity 78 todispose the structure 12 within the inner surface 80 of the head 10. Thestructure 12 is typically turned or rotated such that the axis C isperpendicular to the axis B of the head 10 during insertion of thestructure 12 into the head 10. Then, after the retaining andarticulating structure 12 is within the cavity 78, the retaining andarticulating structure 12 is rotated approximately 90 degrees such thatthe axis C is coaxial with the axis B of the head 10, and then thestructure 12 is seated in sliding engagement with the seating surface 82of the head 10.

The shank capture structure 8 is preloaded, inserted or bottom-loadedinto the head 10 through the bore 84 defined by the neck 83. In otherembodiments according to the invention (not shown), the shank 4 may besized and configured to be top-loaded, if desired in which case it mustbe inserted prior to the retaining and articulating structure 12. Theretaining and articulating structure 12, now disposed in the head 10 iscoaxially aligned with the shank capture structure 8 so that the helicalv-shaped thread 36 rotatingly mates with the thread 98 of the retainingand articulating structure 12.

The shank 4 and/or the retaining and articulating structure 12 arerotated to fully mate the structures 36 and 98 along the respectivecylindrical surfaces 34 and 96, fixing the capture structure 8 to theretaining and articulating structure 12, until the annular top surface38 of the capture structure 8 and the retaining and articulatingstructure top surface 92 are contiguous. Permanent, rigid engagement ofthe capture structure 8 to the retaining and articulating structure 12may be further ensured and supported by the use of adhesive, a spotweld, a one-way thread or deforming one or both of the threads 36 and 98with a punch or the like.

With reference to FIG. 9, at this time the shank 4 is in slidable androtatable engagement with respect to the head 10, while the capturestructure 8 and the lower aperture or neck 83 of the head 10 cooperateto maintain the shank body 6 in rotational relation with the head 10.According to the embodiment of the invention shown in FIGS. 1-28, onlythe retaining and articulating structure 12 is in slidable engagementwith the head spherical seating surface 82. Both the capture structure 8and threaded portion of the shank body 6 are in spaced relation with thehead 10. The shank body 6 can be rotated through a substantial angularrotation relative to the head 10, both from side to side and from frontto rear so as to substantially provide a universal or ball joint whereinthe angle of rotation is only restricted by engagement of the neck 26 ofthe shank body 6 with the neck or lower aperture 83 of the head 10. Itis foreseen that in some embodiments that the retaining structure couldsimply keep the shank upper portion in the receiver and not articulatewith the shank upper portion. In such embodiments, the shank upperportion could have a spherical enlargement that articulates with thehead spherical seating surface, the insert and the retaining structureitself.

The insert 14 is then loaded into the head 10 as illustrated in FIGS. 1and 2 and further operationally shown in FIGS. 9-11. With particularreference to FIG. 10, the insert U-shaped channel 114 is aligned withthe head 10 U-shaped channel 56 and the insert 14 is initiallyside-loaded into the head 10 with the ratchet teeth 124 disposedadjacent to the surfaces 87 and directly above the ratchet teeth 89 ofthe insert receiving surface 88. Such placement allows for unrestrictedangular rotation of the shank body 6 with respect to the head 10. Asillustrated in FIG. 11, the insert 14 may be pushed downward intocontact with the domed top 42, frictionally engaging the top 42 with theinsert 14 and thus setting the angle of orientation of the shank body 6with respect to the head 10 at any desired angle. Because of theorientation of the insert ratchet teeth 124 and the bone screw headratchet teeth 89, the insert 14 is readily and easily pushed downwardinto the head and toward the domed top 42, setting or fixing the desiredangle of orientation between the shank body 6 and the head 10. Again,this can be done directly with a tool or by compression through the rod21. Furthermore, the cooperating ratchet teeth 124 and 89 resist anyupward, loosening forces, as will be described more fully below. Asshown in FIG. 11, a full range of articulation is possible utilizing theinsert 14, also due to the cooperation of the sloped, faceted surfaces120, 134, of the insert 14 and also the inclined top surface 92 of theretaining and articulating structure 12.

With reference to FIG. 10, and also FIGS. 12-18, the assembly 1 istypically screwed into a bone, such as the vertebra 15, by rotation ofthe shank 4 using the driving tool 31 that operably drives and rotatesthe shank 4 by engagement thereof with the insert 14 and the transverseslot 106 of the retaining and articulating structure 12. Specificallywith reference to FIGS. 14-16, the tool 31 shown in FIGS. 12 and 13 isinserted into the head 10 of the bone screw fitted with an insert thathas been loosely placed in the head 10 as shown in FIG. 10. The surface166 of the driving tool 31 comes into contact with the bottom seatingsurface 116 of the insert 14 and the tool arms 164 extend through theinsert notches 136, pushing the insert down into the head 10 until thetool extensions 168 seat within the transverse slot 106 with the toolbottom surface 170 frictionally engaging the base 171 defining thetransverse slot 106. As illustrated in FIG. 16, some frictionalengagement between the tool surface 174 and the top surface 38 of thecapture structure 8 may also be achievable during rotation of thedriving tool 31. It is foreseen that in other embodiments according tothe invention, the transverse slot 106 may be replaced by other types oftool engaging recesses.

Preferably prior to implantation of the bone screw assembly 1 into thevertebra 15, the set screw 206 is assembled with the fastener 204. Withparticular reference to FIGS. 19-21, the Allen-type tool 290 is insertedthrough the bore 254 of the fastener 204 and into the aperture 286 ofthe set screw 206 until seated on the bottom surface 289, with facetedouter surfaces 292 of the tool 290 engaging the inner faceted walls 288of the set screw 206. The set screw 206 is then uploaded into thefastener 204 by rotation of the set screw 206 with respect to thefastener 204 to mate the set screw thread 280 with the fastener innerthread 256 until the set screw top surface 276 abuts the abutmentshoulder 260, resulting in the nested arrangement of the fastener 18shown in FIG. 21, with the set screw 206 completely enveloped in thefastener base 208. The nested assembly 18 shown in FIG. 21 is nowpre-assembled and ready for use with a bone screw head 10 andcooperating rod 21. As illustrated in FIG. 21, in such a pre-assemblyarrangement, the V-ring 270 preferably projects beyond the point 282 andthe V-ring 284 of the set screw 206, such that the base 208 will seatfully within the bone screw arms 52 prior to engagement of the set screw206 with the rod 21.

Typically at least two and up to a plurality of bone screw assemblies 1are implanted into vertebrae for use with the rod 21. With reference toFIGS. 17 and 18, each vertebra 15 may be pre-drilled to minimizestressing the bone and have the guide wire or pin 49 inserted thereinthat is shaped for the cannula 44 of the bone screw shank 6 and providesa guide for the placement and angle of the shank 4 with respect to thevertebra 15. A further tap hole may be made using a tap with the guidewire 49 as a guide. Then, the assembly 1 and the driving tool 31 arethreaded onto the guide wire by first threading the wire into the bottomopening 46 of the shank body 6. The wire 49 is then threaded out of thetop opening 48 and through the bore 142 of the insert 14 and then intothe bore 176 of the driving tool 31. The shank body 6 is then driveninto the vertebra 15, by rotation of the driving tool 31, using the wire49 as a placement guide.

With reference to FIG. 22, the rod 21 is eventually positioned withinthe head U-shaped channel 56, and the nested fastener 18 is theninserted into and advanced between the arms 52. With reference to FIG.23, before or after rod insertion, it may be desirable to move theinsert 14 to a position disengaged from the shank domed top 42 to allowfor rotation of the shank body 6 with respect to the head 10 to adesired angle of articulation. As illustrated in FIG. 23, themanipulation tool 146 may be utilized for such purpose by inserting theprongs 147 of the tool 146 into the opposing bores 68 and pinching orsqueezing the insert arms 112 toward one another to release the insertratchet teeth 124 from the ratchet teeth 89 disposed on the head 10, andthen move the insert 14 up and away from the domed top 42. The tool 146may also be used to lower the insert 14 into position against the domedtop 42. The bores 68 are preferably configured with an oblongorientation such that the insert 14 may be accessed for upward anddownward positioning. Thus, utilizing the insert 14, a bone screwassembly 1 may be set and fixed at a desired angle of articulation priorto implantation of the rod 21, or after the rod 21 is placed in the head10. Furthermore, if it is desired for the bone screw shank to remainrotatable with respect to the head 10 during part or all of a procedureuntil the rod 21 and bone screw assembly 1 are clamped into finalposition with the fastener 18, the insert 14 may be manipulated as shownin FIG. 23 to provide for such freedom of articulation.

With reference to FIG. 24, the insert 14 is pressed downwardly intoengagement with the shank domed top surface 42 to set the angle ofarticulation of the shank body 6 with respect to the head 10 at theposition shown. The rod 21 is seated on the insert 14 and the fastener18 is initially placed between the arms 52 and rotated using theinstallation tool 221 engaged with the surfaces 220 of the break-offhead 210 until the fastener guide and advancement structure 252 is fullymated with the head guide and advancement structure 62, but with the setscrew 206 in position within the fastener base 208 such that the point282 and the ring 284 are not engaged with the rod 21. With reference toFIG. 25, the break-off head 210 is then twisted to a preselected torque,for example 90 to 120 inch pounds, also utilizing the tool 221 inengagement with the faceted outer surface 220 of the break-off head 210,with or without bending of the rod 21 in order to achieve and maintain adesired alignment of the spine.

With reference to FIGS. 26 and 27, thereafter, the set screws 206 aretightened, preferably in a selected order, by inserting the Allen-typetool 290 into the aperture 286 and rotating the tool 290 to thread theset screw 206 downwardly toward the rod 21. As each set screw 206 istorqued tightly using the tool 290, first the point 282 and thenportions of the V-ring 284 preferably come into contact and abrade ordig into the rod surface 108.

As previously discussed herein, because the rod 21 may be bent, not allprojected portions of the fastener base 208 and the set screw 206 maycome into contact with the rod 21. The availability of multiplelocations of engagement of the fastener base 208 and the set screw 206with the rod 21 increases the probability that the rod 21 will beengaged securely by the nested fastener assembly 18. It is noted thatthe fastener base 208 may only seat at the bottom of the bone screw headopening 57 so as to close the opening 57 and capture the rod 21 thereinwithout the V-ring 270 or the base 268 contacting the rod surface 108.The set screw 206 is then turned and tightened against the rod 21, thepoint 284 engaging the rod surface 108 and thereby securing the rod 21in place.

FIG. 27 illustrates the polyaxial bone screw assembly 1 and includingthe rod 21 and the nested fastener 18 positioned in a vertebra 15. Theaxis A of the bone shank 4 is illustrated as not being coaxial with theaxis B of the head 10 and the shank 4 is fixed in this angular lockedconfiguration. Other angular configurations can be achieved, as requiredduring installation surgery due to positioning of the rod 21 or thelike. It is noted that in the illustrated embodiment, the shank domedtop 42 is rounded to approximately equally extend upward into thechannel 56 approximately the same amount no matter what degree ofrotation exists between the shank 4 and head 10 and the surface 42 issized to extend slightly upwardly into the U-shaped channel 56. Thus,the surface 42 is engaged by the insert 14 that is in turn engaged bythe rod 21 and pushed downwardly toward the base 50 of the head 10 whenthe nested fastener 18 biases downwardly toward and onto the rod 21.However, it is foreseen that the thickness of the insert 14 may beincreased to allow for a shank top that does not extend into theU-shaped channel 56.

The downward pressure on the shank 4 pressed upon by the insert 14 inturn urges the retaining and articulating structure 12 downward towardthe head seating surface 82, with the retaining and articulatingstructure outer surface 104 in frictional engagement with the headseating surface 82. As the nested fastener 18 presses against the rod21, the rod 21 presses against the shank and the retaining andarticulating structure 12 that is now rigidly attached to the shank 4which in turn becomes frictionally and rigidly attached to the head 10,fixing the shank body 6 in a desired angular configuration with respectto the head 10 and the rod 21.

With reference to FIG. 28, if removal of the assembly 1 is necessary, orif it is desired to release the rod 21 at a particular location,disassembly is accomplished by using the Allen-type driving tool 290,mated with the set screw 206 at the aperture 286 and turned in adirection to rotate the set screw 206 up and out of the base 208. Theset screw top 276 then backs into and abuts the abutment shoulder 260,transferring rotational torque exerted from the tool 290 from the setscrew 206 to the fastener base 208. The base 208 then rotates with theguide and advancement structure 252 threading out of the guide andadvancement structure 62 of the head 10. Thus, both the set screw 206and the fastener base 208 are removed from the bone screw head 10 at thesame time. If desired, the manipulation tool 146 may be used as shown inFIG. 23 and previously described herein to disengage the insert 14 fromthe shank domed top 42. Finally, disassembly of the assembly 1 isaccomplished in reverse order to the procedure described previouslyherein for assembly.

With reference to FIGS. 29-42, the reference number 301 generallyrepresents a second or alternative embodiment of an assembly accordingto the present invention. The assembly 301 includes a bone screw shank304, having a capture structure 306 and a shank body 308 with a thread310 for threadably implanting into a bone, such as a vertebra 313, and ahead or receiver 314 which connects with the shank 304 to engage andsecure a structural member, such as a spinal fixation rod 316, relativeto the vertebra 313. The assembly 301 also includes a retaining andarticulating structure or ring 320 operably positioned within the heador receiver 314 and engaging the capture structure 306 on the upperportion of the shank 304. The capture structure 306 is retained withinthe head or receiver 314 by the retaining and articulating structure 320as will be described more fully below. The assembly 301 further includesa pressure insert 324, engageable with the upper portion of the capturestructure 306 and the rod 316 as will be described more fully below. Theshank 304, head or receiver 314, retaining and articulating structure320 and the insert 324 are preferably assembled prior to implantation ofthe shank body 308 into the vertebra 313.

With reference to FIG. 42, the assembly 301 further includes a closuretop 326 for fixing the rod 316 within the head or receiver 314. Theinsert 324 allows for setting an angle of articulation between the shankbody 308 and the head or receiver 314 prior to insertion of the rod 316,if desired. Upon installation, which will be described in detail below,the closure top 326 presses against the rod 316 that in turn pressesagainst the insert 324 that presses against the upper end of the capturestructure 306 which biases the retaining and articulating structure 320into fixed frictional contact with the head or receiver 314, so as tofix the rod 316 relative to the vertebra 313. The head or receiver 314and shank 304 cooperate in such a manner that the head or receiver 314and shank 304 can be secured at any of a plurality of angles,articulations or rotational alignments relative to one another andwithin a selected range of angles both from side to side and from frontto rear, to enable flexible or articulated engagement of the head orreceiver 314 with the shank 304 until both are locked or fixed relativeto each other.

Referring to FIGS. 29, 36-38 and 40, the shank 304 is elongated andsized and shaped to be screwed into one of the vertebra 313. The shankbody 308 includes the external helically wound thread 310 that extendsfrom an outer tip 330 to a neck 332 disposed adjacent the capturestructure 306.

On the illustrated shank 304, the capture structure 306 includes aregion 334 that is frusto-conical in shape, diverging in diameter in adirection away from the outer tip 330 and that is coaxially aligned withan axis of rotation of the shank body 308. The region 334 terminates atan annular seating surface 335. The illustrated capture structure 306has a maximum radius that is less than a radius associated with theshank thread 310 and further, preferably less than the radius of theshank body 308 whereupon the thread 8 is located.

The capture structure 306 has a plurality of tool engageable grooves,apertures or the like 336 to enable positive engagement by anappropriately shaped installation tool 338 to thread and drive the shankbody 308 into the vertebra 313 as will be discussed in greater detailbelow. The illustrated shank capture structure 306 includes four evenlyspaced tool engageable grooves 336, but it is foreseen that the drivingstructure may include fewer grooves, an alternative configuration ofgrooves or other driver receiving structure. An upper end surface 340 ofthe capture structure 306 opposite the tip 330 is provided with aformation or dome 342 to be positively and interferingly engaged by theinsert 324, which in turn is positively engaged by the rod 316 when theassembly 301 is assembled into place. The illustrated dome 342 isradiused, knurled and centered on the upper end surface 340 so as to becoaxial with the remainder of the shank 304. The scoring or knurling ofthe dome 342 operably frictionally abuts against the insert 324 when theinsert 324 is rotated into engagement with the head or receiver 314, asdescribed more fully below, to provide for a selected setting of adesired angle of articulation between the shank body 308 and the head314 prior to insertion and locking down of the rod 315. It is foreseenthat in certain embodiments, the purpose of the dome 342 is simply to beengaged by the insert 324 that is in turn engaged by the rod 316,pushing the shank 304 in such a manner as to frictionally engage theretaining and articulating structure 320 with the head 314 as describedbelow. Preferably, the dome 342 is radiused so that the dome 342 engagesthe insert 324 at approximately the same location regardless of theangle of articulation of the shank body 308 with respect to the head314. However, it is foreseen that in certain embodiments shapes otherthan the dome 342 could be utilized.

Referring to FIGS. 29-31, and 36-42, the head or receiver 314 isgenerally cylindrical in external profile and has a central and axiallyaligned shank receiving bore 346 ending at an inner and lower neck 347.The neck 347 is radiused to receive the shank capture structure 306 andpreferably smaller than a radius of the shank body 308 and thread 310.The bore 346 is also preferably sized larger than the capture structure306 of the shank 304 to enable the shank 394 to be oriented through arange of angular dispositions relative to the head or receiver 314. Thebore 346 may be conically counterbored or beveled in a region 348 towiden the angular range of the shank 304.

The head or receiver 314 is provided with a U-shaped rod cradle 350sized to receive the rod 316 therethrough. The illustrated cradle 350 isrounded and radiused at an inner or lower portion or seat 352 to snuglymate with a cylindrical outer surface 354 of the rod 316 and open at anouter end or top 356, with spaced apart side surfaces 358 so as to formupstanding and spaced apart arms 360. The side surfaces 358 have guideand advancement structures 362 formed thereon that are complementary toguide and advancement structures 364 of the closure top 326 (FIG. 42).The illustrated structures 362 and 364 are helically wound flanges orthreads that advance the closure top 326 into the head 314, as theclosure top 326 is rotated about a central axis thereof. It is foreseenthat the structures 362 and 364 may be interlocking helical flange formssimilar to the structures 62 and 252 previously described herein withrespect to the assembly 1, V-shaped threads, buttress threads, squarethreads, reverse angle threads, or other types of threads or flangeforms. Preferably, the structures 362 and 364 are of such a nature as toresist splaying of the arms 360 when the closure top 326 is advancedinto the U-shaped cradle 350.

Furthermore the head or receiver 314 includes an assembly cavity 366formed therein that opens into the cradle 350. A partially sphericalsocket or seat 368 defines the assembly cavity 366. The seat 368 isdisposed between the arm inner surfaces 358 and the neck 347 definingthe shank bore 346 and as illustrated has a radius that is slightly lessthan a radius of the assembly cavity 366. The seat 368 has asubstantially spherical shape and extends upward coaxially through thehead 314 from the neck 347 to the cavity 366. The cavity 366 and theseat 368 will be detailed further below.

Each arm inner surface 358 further includes a recessed portion 370disposed between the guide and advancement structure 362 and the seat368. The portion 370 is defined by an upper shoulder 372, a lowershoulder 374 and a wall 376 disposed between the upper and lowershoulders 372, 374. The wall 376 is parallel to an axis of rotation ofthe head 314 that is operably coaxial with the shank 304. As will bedescribed in greater detail below, the insert 324 may be operablydisposed in the recessed portion 370 and include a setting positionwherein the insert 324 abuts against the upper shoulder 372 and pressesagainst the shank capture structure dome 342, allowing for the settingof a desired angle of articulation of the bone screw shank body 308 withrespect to the head 314 during surgery, prior to lock down of the rod316 by the closure top 326. The head or receiver 314 may further includeexternal, closed end grip bores 378 for positive engagement by a holdingtool (not shown) to facilitate secure gripping of the head 314 duringassembly, installation and/or manipulation of the assembly 301.

The retaining and articulating structure 320, best illustrated in FIGS.29-31 and 36 is used to retain the capture structure 306 within the heador receiver 314. The retaining and articulating structure 320 is in theform of a discontinuous ring that resiliently expands and contracts toenable the structure 320 to be snapped over and seated on the capturestructure 306. The retaining and articulating structure 320, similar toa remainder of the assembly 301, is preferably formed of a material suchas a spring stainless steel, tantalum, titanium or other resilientimplantable material. The illustrated retaining and articulatingstructure 320 forms a gap or radial split 380 extending from a topsurface 382 to a bottom surface 384 thereof, that allows the structure320 to expand in circumference to fit over the capture structure 306.The retaining and articulating structure 320 includes an inner surface382 formed by a through-bore sized and shaped to be compatible with theconical shape of the capture structure 306. The retaining andarticulating structure 320 has an outer surface that isfrusto-spherical, partially spherical, or a segment of a sphere, with aspherical radius approximately equivalent to the spherical radius of thespherical seat 368 within the head 314 and smaller than a radius of thecavity 366. As will be described more fully below, the bottom surface384 seats upon the annular seating surface 335 of the shank capturestructure 306 when the retaining and articulating structure 320 is fullyinstalled on the capture structure 306.

The closure top 326 is generally cylindrical in shape and is providedwith a break-off head 390 that is connected to the closure top 326 by aweakened area or neck 392 such that the break-off head 390 separatesfrom the closure top 326 at a predetermined torque applied to thebreak-off head 390 during assembly. The illustrated break-off head 390has a hexagonal cross section for engagement by a tool (not shown) of acomplementary shape. The closure top 326 further includes a centralpoint 394 for abrading and/or penetrating the rod 316 when fullyinstalled on the head 314. Furthermore, the closure top 326 includes adriving formation, such as a hex aperture (not shown) for removal of theclosure top, if desired, after the break-off head 390 is broken off.

The insert 324 is best illustrated in FIGS. 32-35. The insert 324includes a substantially conical base portion 401 integral with a bodyportion 404. The base portion 401 extends outwardly from an annular,flat bottom surface 402 to the body portion 404. The body portion 404 isoblong, having a width W that is smaller than a length L thereof. Thewidth W is bounded by two substantially flat surfaces 405. The width Wis slightly smaller than a distance between the inner surfaces of thearms 358 of the head 314. The length L, taken along a center line 406 isslightly smaller than a diameter of the recessed portion 370 measuredbetween the surfaces 376. A U-shaped cradle or channel 407 runningparallel to the width W extends through the body portion 404, and issized and shaped to receive the rod 316 thereon as will be describedmore fully below. Arms 408 disposed on either side of the cradle 406each included a top surface 410 that is parallel to the bottom surface402 and a sloped surface 412, starting at the top surface 410 andsloping downwardly toward the base portion 401. The arms 408 alsoinclude rounded, substantially cylindrical side surfaces 414, eachhaving a radius slightly smaller than a radius of the wall 376 thatpartially defines the recessed portion 370 of the head 314. The slopedsurfaces 412 are disposed opposite one another and the top surfaces 410are disposed opposite one another. The sloped surfaces 412 also slope inopposite directions, each starting at the center line or axis 406 andrunning outwardly and downwardly away therefrom to provide for a camaction when the insert 324 is placed in the head 314 as shown in FIG.37, and then rotated, the sloped surfaces 412 engaging the uppershoulder 372 of the recessed portion 370 of the head 314 and thustransforming the circular motion of rotating the insert 324 in therecessed portion 370 of the head 314 into linear motion, pressing theinsert 324 against the shank dome 342 as will be described more fullybelow.

Each arm 408 of the body portion 404 includes a substantially flatbottom surface 416 extending from the conical base portion 401 to thecylindrical surface 414. The base portion 401 further includes acentrally located concave, substantially spherical bottom formation 418contiguous to the annular bottom surface 402. The spherical bottomformation 418 is sized and shaped to cooperate and engage with the dome342 of the shank capture structure 306, providing a snug, frictionalfit. Apertures 420 extend through the U-shaped cradle 407 and are sizedand shaped to cooperate and align with the apertures 336 of the capturestructure 306. Thus, in the illustrated embodiment, four evenly spacedapertures 420 extend through the insert 324 and axially align with theapertures 336 as illustrated in FIGS. 39 and 40, both when the insert324 is initially placed in the head 314 and when the insert 324 isrotated within the head 314 such that the top surfaces 410 are adjacentthe upper shoulder 371. Alignment of the apertures 420 and the apertures336 allow for engagement between the capture structure 306, the insert324 and the driving tool 338 as will be described more fully below.

The driver 338 illustrated at FIG. 40 includes a handle (not shown), adrive shaft 426 and an engagement portion 428. The engagement portion426 includes an oblong support 430 sized and shaped to fit within theU-shaped cradle 407 of the insert 324. Four prongs 432 extending fromthe oblong support 430 are sized and shaped to extend through theapertures 420 of the insert 324 and into the apertures 336 in thecapture structure 306, thus operably engaging both the bone screw shank304 and the insert 324 when rotating and driving the shank body 308 intothe vertebra 313.

FIGS. 30, 31 and 36 illustrate the assembly of the bone screw head 314,shank 304 and retaining and articulating structure 320. In FIG. 30, theretaining and articulating structure 320 is inserted into the head 314through an interior of the U-shaped cradle 350. The retaining andarticulating structure 320 is first oriented with a central axis thereofat a right angle to a central axis of the bore 346. Then, the retainingand articulating structure is oriented as illustrated in FIG. 31 withthe central axis of the retaining and articulating structure 320 beingparallel or coincident with the axis of the bore 346 and the neck 347,by rotating the retaining and articulating structure 320 within theassembly cavity 366. With reference to FIG. 36, the capture structure306 of the shank 304 is then inserted through the head bore 346 and thenadjacent to the retaining and articulating structure inner surface 386by expanding the retaining and articulating structure 320 at the radialsplit 380 so as to snap the retaining and articulating structure 320over and around the capture structure 306 at the frusto-conical surface334. The relative resistance encountered by the retaining andarticulating structure 320 allows the capture structure 306 to expandthe circumference of the retaining and articulating structure 320, byexpansion of the split 380, so that the capture structure 306 enters theretaining and articulating structure 320. As illustrated in FIG. 37,when fully seated, the surface 334 frictionally engages the retainingand articulating structure inner surface 386 and the bottom surface 384of the retaining and articulating structure 320 abuts against theannular seating surface 335 of the capture structure 306 therebylimiting penetration of the capture structure 306 into the retaining andarticulating ring structure 320.

FIG. 37 shows the assembly 301 with the retaining and articulatingstructure 320 lowered from the assembly position and positioned in thespherical seat 368 with the central axis of the shank 304 coaxial withthe central axis of the head 314. However, similar to the assembly 1,the relevant discussion of which is incorporated by reference herein,the curved or spherical seat 368 and the curved or spherical outersurface 388 of the retaining and articulating structure 320, allowsuniversal angular positioning of the shank 304 relative to the head 314.The retaining and articulating structure 320, thus performs thefunctions of preventing the capture structure 306 of the shank 304 fromslipping through the neck 347 and, in conjunction with the seat 368,forms a ball joint for relative orientation of the shank 304 and thehead 314.

The insert 324 is then loaded into the head 314 as illustrated in FIGS.37 and 39, with the width dimension W being oriented as shown withrespect to the arms 360 to allow top loading of the insert 324. Theinsert 324 is lowered into the head 314 until the concave bottomformation 418 is seated on the dome 342.

For driving the bone screw shank body 308 into bone, such as thevertebra 313, the insert 324 is first rotated axially as illustrated inFIGS. 40 and 41, with the sloping surfaces 412 of the insert 324contacting the upper shoulder 372 defining the head recessed portion370, thereby pushing the capture structure 306 and attached retainingand articulating structure 320 downwardly against the seat 368. As theinsert is rotated approximately 90 degrees until the flat surfaces 410fully engage the upper shoulder 372, the insert 324 functions as a cam,providing a mechanical linkage that converts rotary motion to linearmotion. Frictional engagement between the retaining and articulatingstructure 320 and the seat 368 sets the bone shank 304 in an angularposition with respect to the head 314, but does not lock such intoposition. Thus, the insert 324 may be used at any time during aprocedure to set the shank body 308 at a desired angle with respect tothe head 314, but that position is not rigidly fixed until the rod 316presses down upon the insert 324. When the insert flat surfaces 410engage the upper shoulder 372, the apertures 420 of the insert 324 arealigned with the apertures 336 of the capture structure 306 and theinsert cradle 407 is oriented in a position to receive the oblongsupport 430 of the driving tool engagement portion 428.

With particular reference to FIG. 40, the assembly 301 is typicallyscrewed into a bone, such as the vertebra 313, by rotation of the shank304 using the driving tool 338 that operably drives and rotates theshank 304 by engagement thereof with the insert 324 and the apertures336 of the capture structure 306. The driving tool 338 is inserted intothe head 314 of the bone screw with the prongs 432 first inserted intothe apertures 420 and then the apertures 336 until the oblong support430 is seated on the insert cradle 407.

Typically at least two and up to a plurality of bone screw assemblies301 are implanted into vertebrae for use with the rod 316. As describedwith respect to the assembly 1, and incorporated by reference herein,each vertebra 313 may be pre-drilled to minimize stressing the bone.Although not shown, the assembly 301 may be cannulated in a manner asdescribed with respect to the assembly 1 so that a guide wire or pin maybe used as a guide for the placement and angle of the assembly 301. Theshank body 308 is then driven into the vertebra 313, by rotation of thedriving tool 338.

With reference to FIG. 42, the rod 316 is eventually positioned withinthe head U-shaped rod cradle 350, and the closure top 326 is theninserted into and advanced between the arms 360. Before rod insertion,it may be desirable to rotate the insert 324 to a position disengagedfrom the shank domed top 342 as shown in FIG. 37, to allow for a looseangular connection of the shank body 308 with respect to the head 314until a desired angle of articulation is decided upon. The driving tool338 may be utilized to rotate the insert 324 by inserting the prongs 432in the apertures 420. Then, the insert 324 may be rotated to theposition shown in FIG. 41, setting, but not locking such desired angularorientation between the shank body 308 and the head 314. In other words,when the insert 324 is in contact with the upper shoulder 372, theinsert 324 presses down on the shank 304, providing sufficientfrictional engagement between the retaining and articulating structure320 and the head seat 368 that the shank 304 resists angular movement.However, it may not be desirable to rotate the insert 324 in order tochange the angular orientation of the shank 304 with respect to the head314. The shank 304 may simply be moved, using some force, to a desiredposition, which will then be the set position.

With reference to FIG. 24, the rod 316 is seated on the insert 324 andthe closure top 326 is initially placed between the arms 360 and rotatedusing an installation tool (not shown) engaged with surfaces of thebreak-off head 390 until the guide and advancement structure 364 isfully mated with the head guide and advancement structure 262, with thepoint 394 penetrating the rod 316. The break-off head 390 is thentwisted to a preselected torque, for example 90 to 120 inch pounds,until broken off.

If removal of the assembly 301 is necessary, or if it is desired torelease the rod 316 at a particular location, disassembly isaccomplished by using a tool (not shown) with a driving formation (notshown) located on the closure top 326 to rotate and remove the closuretop 326 from the head 314. Disassembly of the assembly 301 isaccomplished in reverse order to the procedure described previouslyherein for assembly.

With reference to FIGS. 43-54, the reference number 501 generallyrepresents a third embodiment of an assembly according to the presentinvention. The assembly 401 includes a bone screw shank 504, having acapture structure 506 and a shank body 508 with a thread 510 forthreadably implanting into a bone, such as a vertebra 513, and a head orreceiver 514 which connects with the shank 504 to engage and secure astructural member, such as a spinal fixation rod 516, relative to thevertebra 513. The assembly 501 also includes a retaining andarticulating structure or ring 520 operably positioned within the heador receiver 514 and engaging the capture structure 506 of the shank 504.The capture structure 506 is retained within the head or receiver 514 bythe retaining and articulating structure 520 as will be described morefully below. The assembly 501 further includes a pressure insert 524,engageable with the capture structure 506 and the rod 516 as will bedescribed more fully below. The shank 504, head or receiver 514,retaining and articulating structure 520 and the insert 524 arepreferably assembled prior to implantation of the shank body 508 intothe vertebra 513.

With reference to FIG. 54, the assembly 501 further includes a closuretop 526 for fixing the rod 516 within the head or receiver 514. Theinsert 524 allows for setting an angle of articulation between the shankbody 508 and the head or receiver 514 prior to insertion of the rod 516,if desired. Upon installation, which will be described in detail below,the closure top 526 presses against the rod 516 that in turn pressesagainst the insert 524 that presses against the capture structure 506which biases the retaining and articulating structure 520 into fixedfrictional contact with the head or receiver 514, so as to fix the rod516 relative to the vertebra 513. The head or receiver 514 and shank 504cooperate in such a manner that the head or receiver 514 and shank 504can be secured at any of a plurality of angles, articulations orrotational alignments relative to one another and within a selectedrange of angles both from side to side and from front to rear, to enableflexible or articulated engagement of the head or receiver 514 with theshank 504 until both are locked or fixed relative to each other.

Referring to FIGS. 43, 46-48 and 52, the shank 504 is elongated andsized and shaped to be screwed into one of the vertebra 513. The shankbody 508 includes the external helically wound thread 510 that extendsfrom an outer tip 530 to a neck 532 disposed adjacent the capturestructure 506.

On the illustrated shank 504, the capture structure 506 includes asubstantially cylindrical threaded region 534 that is coaxially alignedwith an axis of rotation of the shank body 508. The region 534terminates at an annular seating surface 535. The illustrated capturestructure 506 has a maximum radius that is less than a radius associatedwith the shank thread 510.

The capture structure 506 has a plurality of tool engageable grooves,apertures or the like 536 to enable positive engagement by anappropriately shaped installation tool 538 to thread and drive the shankbody 508 into the vertebra 513 as will be discussed in greater detailbelow. The illustrated shank capture structure 506 includes four evenlyspaced tool engageable grooves 536, but it is foreseen that the drivingstructure may include fewer grooves, an alternative configuration ofgrooves or other driver receiving structure. An upper end surface 540 ofthe capture structure 506 opposite the tip 530 is provided with aformation or dome 542 to be positively and interferingly engaged by theinsert 524, which in turn is positively engaged by the rod 516 when theassembly 501 is assembled into place. The illustrated dome 542 isradiused, knurled and centered on the upper end surface 540 so as to becoaxial with the remainder of the shank 504. The scoring or knurling ofthe dome 542 operably frictionally abuts against the insert 524 when theinsert 524 is rotated into engagement with the head or receiver 514, asdescribed more fully below, to provide for a selected setting of adesired angle of articulation between the shank body 508 and the head orreceiver 514 prior to insertion and locking down of the rod 515. It isforeseen that in certain embodiments, the purpose of the dome 542 issimply to be engaged by the insert 524 that is in turn engaged by therod 516, pushing the shank 504 in such a manner as to frictionallyengage the retaining and articulating structure 520 with the head orreceiver 514 as described below. Preferably, the dome 542 is radiused sothat the dome 542 engages the insert 524 at approximately the samelocation regardless of the angle of articulation of the shank body 508with respect to the head or receiver 514. However, it is foreseen thatin certain embodiments shapes other than the dome 542 could be utilized.In the embodiment shown in FIGS. 43-54, the upper end 540 supporting thedome 542 has a hex-shaped profile with side surfaces 543 configured tomate with an assembly or driving tool (not shown).

Referring to FIGS. 43-48, the head or receiver 514 is generallycylindrical in external profile and has a central and axially alignedshank receiving bore 546 ending at an inner and lower neck 547. The neck547 is radiused to receive the shank capture structure 506 andpreferably smaller than a radius of the shank body 508 and thread 510.The bore 546 is also preferably sized larger than the capture structure506 of the shank 504 to enable the shank 594 to be oriented through arange of angular dispositions relative to the head or receiver 514. Thebore 546 may be conically counterbored or beveled in a region 548 towiden the angular range of the shank 504.

The head or receiver 514 is provided with a U-shaped rod cradle 550sized to receive the rod 516 therethrough. The illustrated cradle 550 isrounded and radiused at an inner or lower portion or seat 552 to snuglymate with a cylindrical outer surface 554 of the rod 516 and open at anouter end or top 556, with spaced apart side surfaces 558 so as to formupstanding and spaced apart arms 560. The side surfaces 558 have guideand advancement structures 562 formed thereon that are complementary toguide and advancement structures 564 of the closure top 526 (FIG. 54).The illustrated structures 562 and 564 are helically wound flanges orthreads that advance the closure top 526 into the head or receiver 514,as the closure top 526 is rotated about a central axis thereof. It isforeseen that the structures 562 and 564 may be interlocking helicalflange forms similar to the structures 62 and 252 previously describedherein with respect to the assembly 1, V-shaped threads, buttressthreads, reverse angle threads, or other types of threads or flangeforms. Preferably, the structures 562 and 564 are of such a nature as toresist splaying of the arms 560 when the closure top 526 is advancedinto the U-shaped cradle 550.

Furthermore the head or receiver 514 includes an assembly cavity 566formed therein that opens into the cradle 550. A partially sphericalsocket or seat 568 defines the assembly cavity 566. The seat 568 isdisposed between the arm inner surfaces 558 and the neck 547 definingthe shank bore 546 and as illustrated has a radius that is slightly lessthan a radius of the assembly cavity 566. The seat 568 has asubstantially spherical shape and extends upward coaxially through thehead or receiver 514 from the neck 547 to the cavity 566. The cavity 566and the seat 568 will be detailed further below.

Each arm inner surface 558 further includes a recessed portion 570disposed between the guide and advancement structure 562 and the seat568. The portion 570 is defined by an upper shoulder 572, a lowershoulder 574 and a wall 576 disposed between the upper and lowershoulders 572, 574. The wall 576 is parallel to an axis of rotation ofthe head or receiver 514 that is operably coaxial with the shank 504. Aswill be described in greater detail below, the insert 524 may beoperably disposed in the recessed portion 570 and include a settingposition wherein the insert 524 abuts against the upper shoulder 572 andpresses against the shank capture structure dome 542, allowing for thesetting of a desired angle of articulation of the bone screw shank body508 with respect to the head 514 during surgery, prior to lock down ofthe rod 516 by the closure top 526. The head or receiver 514 may furtherinclude external, closed end grip bores 578 for positive engagement by aholding tool (not shown) to facilitate secure gripping of the head 514during assembly, installation and/or manipulation of the assembly 501.

The retaining and articulating structure 520, best illustrated in FIGS.43-48 and 54 is used to retain the capture structure 506 within the heador receiver 514. The retaining and articulating structure 520 is in theform of a ring. The retaining and articulating structure 520 includes atop surface 582, a bottom surface 584, an inner surface 586 having athread 587 and an outer surface 588. The thread 587 is sized and shapedto mate with the threaded region 534 of the capture structure 506. Theretaining and articulating structure 520, similar to a remainder of theassembly 501, is preferably formed of a material such as a springstainless steel, tantalum, titanium or other resilient implantablematerial.

The retaining and articulating structure outer surface 588 isfrusto-spherical, partially spherical, or a segment of a sphere, with aspherical radius approximately equivalent to the spherical radius of thespherical seat 568 within the head or receiver 514 and smaller than aradius of the cavity 566. As will be described more fully below, thebottom surface 584 seats upon the annular seating surface 535 of theshank capture structure 506 when the retaining and articulatingstructure 520 is fully installed on the capture structure 506.

The closure top 526 is generally cylindrical in shape and is providedwith a break-off head 590 that is connected to the closure top 526 by aweakened area or neck 592 such that the break-off head 590 separatesfrom the closure top 526 at a predetermined torque applied to thebreak-off head 590 during assembly. The illustrated break-off head 590has a hexagonal cross section for engagement by a tool (not shown) of acomplementary shape. The closure top 526 further includes a centralpoint 594 for abrading and/or penetrating the rod 516 when fullyinstalled on the head 514. Furthermore, the closure top 526 includes adriving formation, such as a hex aperture (not shown) for removal of theclosure top, if desired, after the break-off head 590 is broken off.

The insert 524 is best illustrated in FIGS. 43, 47 and 49-54. The insert524 includes a substantially conical base portion 601 integral with abody portion 604. The base portion 601 extends outwardly from anannular, flat bottom surface 602 to the body portion 604. The bodyportion 604 is oblong, having a width W′ that is smaller than a lengthL′ thereof. The width W′ is bounded by two substantially flat surfaces605. The width W′ is slightly smaller than a distance between the innersurfaces of the arms 558 of the head 514. The length L′, taken along acenter line 606 is slightly smaller than a diameter of the recessedportion 570 measured between the surfaces 576. A U-shaped cradle orchannel 607 running parallel to the width W extends through the bodyportion 604, and is sized and shaped to receive the rod 516 thereon aswill be described more fully below. Arms 608 disposed on either side ofthe cradle 606 each included a top surface 610 that is parallel to thebottom surface 602 and a sloped surface 612, starting at the top surface610 and sloping downwardly toward the base portion 601. The arms 608also include rounded, substantially cylindrical side surfaces 614, eachhaving a radius slightly smaller than a radius of the wall 576 thatpartially defines the recessed portion 570 of the head 514. The slopedsurfaces 612 are disposed opposite one another and the top surfaces 610are disposed opposite one another. The sloped surfaces 612 also slope inopposite directions, each starting at the center line or axis 606 andrunning outwardly and downwardly away therefrom to provide for a camaction when the insert 524 is placed in the head 514 as shown in FIG.49, and then rotated, the sloped surfaces 612 engaging the uppershoulder 572 of the recessed portion 570 of the head 514 and thustransforming the circular motion of rotating the insert 524 in therecessed portion 570 of the head 514 into linear motion, pressing theinsert 524 against the shank dome 542 as will be described more fullybelow.

Each arm 608 of the body portion 604 includes a substantially flatbottom surface 616 extending from the conical base portion 601 to thecylindrical surface 614. The base portion 601 further includes acentrally located concave, substantially spherical bottom formation 618contiguous to the annular bottom surface 602. The spherical bottomformation 618 is sized and shaped to cooperate and engage with the dome642 of the shank capture structure 606, providing a snug, frictionalfit. Apertures 620 extend through the U-shaped cradle 607 and are sizedand shaped to cooperate and align with the apertures 536 of the capturestructure 506.

Thus, in the illustrated embodiment, four evenly spaced apertures 620extend through the insert 524 and axially align with the apertures 536as illustrated in FIGS. 49 and 53, both when the insert 524 is initiallyplaced in the head 514 and when the insert 524 is rotated within thehead 514 such that the top surfaces 610 are adjacent the upper shoulder571. The alignment of the apertures 620 and the apertures 536 as shownin FIG. 53 allow for engagement between the capture structure 506, theinsert 524 and the driving tool 538 as will be described more fullybelow.

A pair of points 622 are disposed in the U-shaped cradle 607 and projecttherefrom. The points 622 are disposed along the center line 606 andnear the surfaces 610 and 612, but could be placed in other areas. Thepoints 622 are sized and shaped to abrade and penetrate the rod 516 aswill be described more fully below. One to six or more points could beutilized.

The driver 538 illustrated at FIG. 52 includes a handle (not shown), adrive shaft 626 and an engagement portion 628. The engagement portion626 includes four prongs 632 extending therefrom sized and shaped toextend through the apertures 620 of the insert 524 and into theapertures 536 in the capture structure 506, thus operably engaging boththe bone screw shank 504 and the insert 524 when rotating and drivingthe shank body 508 into the vertebra 513.

FIGS. 43-47 illustrate the assembly of the bone screw head 514, shank504 and retaining and articulating structure 520. In FIG. 44, theretaining and articulating structure 520 is inserted into the head 514through an interior of the U-shaped cradle 550. The retaining andarticulating structure 520 is first oriented with a central axis thereofat a right angle to a central axis of the bore 546. Then, the retainingand articulating structure is oriented as illustrated in FIG. 45 withthe central axis of the retaining and articulating structure 520 beingparallel or coincident with the axis of the bore 546 and the neck 547,by rotating the retaining and articulating structure 520 within theassembly cavity 566. With reference to FIG. 56, the capture structure506 of the shank 504 is then inserted through the head bore 546 and thenrotated with respect to the retaining and articulating structure 520,mating the threaded region 534 with thread 587 disposed on the innersurface 586 of the retaining and articulating structure 520. Asillustrated in FIG. 47, when fully seated, the bottom surface 584 of theretaining and articulating structure 520 abuts against the annularseating surface 535 of the capture structure 506.

FIGS. 47 and 48 show the assembly 501 with the retaining andarticulating structure 520 lowered from the assembly position andpositioned in the spherical seat 568 with the central axis of the shank504 coaxial with the central axis of the head 514. However, similar tothe assembly 1, the relevant discussion of which is incorporated byreference herein, the curved or spherical seat 568 and the curved orspherical outer surface 588 of the retaining and articulating structure520, allows universal angular positioning of the shank 504 relative tothe head 514. The retaining and articulating structure 520, thusperforms the functions of preventing the capture structure 506 of theshank 504 from slipping through the neck 547 and, in conjunction withthe seat 568, forms a ball joint for relative orientation of the shank504 and the head 514.

The insert 524 is then loaded into the head 514 as illustrated in FIGS.47 and 49, with the width dimension W′ being oriented as shown withrespect to the arms 560 to allow top loading of the insert 524. Theinsert 524 is lowered into the head 514 until the concave bottomformation 618 is seated on the dome 542.

For driving the bone screw shank body 508 into bone, such as thevertebra 513, the insert 524 is first rotated axially as illustrated inFIGS. 52 and 53, with the sloping surfaces 612 of the insert 524contacting the upper shoulder 572 defining the head recessed portion570, thereby pushing the capture structure 506 and attached retainingand articulating structure 520 downwardly against the seat 568. As theinsert is rotated approximately 90 degrees until the flat surfaces 610fully engage the upper shoulder 572, the insert 524 functions as a cam,providing a mechanical linkage that converts rotary motion to linearmotion. Frictional engagement between the retaining and articulatingstructure 520 and the seat 568 sets the bone shank 504 in an angularposition with respect to the head 514, but does not lock such intoposition. Thus, the insert 524 may be used at any time during aprocedure to set the shank body 508 at a desired angle with respect tothe head 514, but that position is not rigidly fixed until the rod 516presses down upon the insert 524. When the insert flat surfaces 610engage the upper shoulder 572, the apertures 620 of the insert 524 arealigned with the apertures 536 of the capture structure 506 and theinsert cradle 607 is oriented in a position to receive the oblongsupport 630 of the driving tool engagement portion 628.

With particular reference to FIG. 52, the assembly 501 is screwed into abone, such as the vertebra 513, by rotation of the shank 504 using thedriving tool 538 that operably drives and rotates the shank 504 byengagement thereof with the apertures 620 of the insert 524 and theapertures 536 of the capture structure 506. The driving tool 538 isinserted into the head 514 of the bone screw with the prongs 632 firstinserted into the apertures 620 and then the apertures 536, and thendriven and rotated into bone.

Alternatively, the assembly 501 may be driven into bone prior toplacement of the insert 524 in the head 514. A hex driving tool (notshown) sized and shaped to mate with the surfaces 543 of the capturestructure 506 may be used to rotate and drive the shank body 508 intothe vertebra 513. Thereafter, the insert 524 may be placed in the bonescrew head 514 as shown in FIG. 47.

Typically at least two and up to a plurality of bone screw assemblies501 are implanted into vertebrae for use with the rod 516. As describedwith respect to the assembly 1, and incorporated by reference herein,each vertebra 513 may be pre-drilled to minimize stressing the bone.Although not shown, the assembly 501 may be cannulated in a manner asdescribed with respect to the assembly 1 so that a guide wire or pin maybe used as a guide for the placement and angle of the assembly 501. Theshank body 508 is then driven into the vertebra 513, by rotation of thedriving tool 538.

With reference to FIG. 54, the rod 516 is eventually positioned withinthe head U-shaped rod cradle 550, and the closure top 526 is theninserted into and advanced between the arms 560. Before rod insertion,it may be desirable to rotate the insert 524 to a position disengagedfrom the shank domed top 542 as shown in FIG. 47, to allow for a looseangular connection of the shank body 508 with respect to the head 514until a desired angle of articulation is decided upon. The driving tool538 may be utilized to rotate the insert 524 by inserting the prongs 632in the apertures 620. Then, the insert 524 may be rotated to theposition shown in FIG. 53, setting, but not locking such desired angularorientation between the shank body 508 and the head 514. In other words,when the insert 5324 is in contact with the upper shoulder 572, theinsert 524 presses down on the shank 504, providing sufficientfrictional engagement between the retaining and articulating structure520 and the head seat 568 that the shank 504 resists angular movement.However, it may not be desirable to rotate the insert 524 in order tochange the angular orientation of the shank 504 with respect to the head514. The shank 504 may simply be moved, using some force, to a desiredposition, which will then be the set position.

With reference to FIG. 54, the rod 516 is seated on the insert 524 andthe closure top 526 is initially placed between the arms 560 and rotatedusing an installation tool (not shown) engaged with surfaces of thebreak-off head 590 until the guide and advancement structure 564 isfully mated with the head guide and advancement structure 562, with thepoint 594 penetrating the rod 516 and also the points 622 penetratingthe rod 516. The break-off head 590 is then twisted to a preselectedtorque, for example 90 to 120 inch pounds, until broken off.

If removal of the assembly 501 is necessary, or if it is desired torelease the rod 516 at a particular location, disassembly isaccomplished by using a tool (not shown) with a driving formation (notshown) located on or in the closure top 526 to rotate and remove theclosure top 526 from the head 514. Disassembly of the assembly 501 isaccomplished in reverse order to the procedure described previouslyherein for assembly.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed is:
 1. A bone anchor assembly for securing an elongaterod to a bone, the bone anchor assembly comprising: a shank having aproximal capture portion and an anchor portion extending distally fromthe proximal capture portion for fixation to the bone; a receiver havinga longitudinal axis, an upper portion defining a U-shaped channel withinner sidewall surfaces configured to receive the elongate rod, and alower portion defining a cavity communicating with the U-shaped channeland a receiver bottom opening, the inner sidewall surfaces including aguide and advancement structure and a discontinuous downward-facingshoulder pre-formed therein between the guide and advancement structureand the bottom opening; and a pressure insert sized and shaped to bepositioned downwardly within the receiver into a first position, thepressure insert having upward-facing contact surfaces and beingrotatable into a second position that locates the upward-facing contactsurfaces at least partially under the receiver discontinuousdownward-facing shoulder to prevent the pressure insert from moving backup within the receiver.
 2. The bone anchor assembly of claim 1, whereinthe pressure insert further comprises a central body havingradially-extending portions that are operable to rotate underneathopposing portions of the receiver discontinuous downward-facing shoulderwhen the pressure insert is rotated about the receiver longitudinalaxis, the radially-extending portions having the upward-facing contactsurfaces formed thereon.
 3. The bone anchor assembly of claim 2, whereinthe upward-facing contact surfaces of the radially-extending portionsinclude a pair of sloped portions operable to engage the opposingportions of the receiver discontinuous downward-facing shoulder as thepressure insert is rotated about the receiver longitudinal axis toprovide a cam action that converts the rotatory motion of the pressureinsert into linear downward movement of the pressure insert.
 4. The boneanchor assembly of claim 3, wherein the upward-facing contact surfacesof the radially-extending portions further include substantiallyhorizontal portions adjacent the sloped portions and operable tofrictionally engage the receiver discontinuous downward-facing shoulderwhen the pressure insert is fully rotated to the second position.
 5. Thebone anchor assembly of claim 4, wherein the pressure insert continuesto rotate toward the second position after the linear downward movementof the pressure insert is complete.
 6. The bone anchor assembly of claim2, wherein the central body of the pressure insert further includes arod-engaging U-shaped cradle formed therein that aligns with theU-shaped channel of the receiver when the pressure insert is fullyrotated to the second position.
 7. The bone anchor assembly of claim 1,wherein the pressure insert engages the shank.
 8. The bone anchorassembly of claim 1, wherein the pressure insert is rotatable into thesecond position with a tool.
 9. The bone anchor assembly of claim 8,wherein an upper surface of the pressure insert includes at least onetool engagement structure complementary with an engagement portion ofthe tool.
 10. The bone anchor assembly of claim 1, wherein the proximalcapture portion of the shank is uploaded through the receiver bottomopening.
 11. The bone anchor assembly of claim 1, further comprising aretainer sized and shaped for loading into the receiver cavity to engageand hold the shank proximal capture portion in spaced relation withrespect to the receiver while an outer surface of the retainer engagesan interior surface of the receiver cavity to allow a pivotal motionbetween the receiver and the shank.
 12. A bone anchor assembly forsecuring an elongate rod to a bone, the bone anchor assembly comprising:a shank having a proximal capture portion with an outer sphericalsurface and an anchor portion extending distally from the proximalcapture portion for fixation to the bone; a receiver having alongitudinal axis, an upper portion defining a U-shaped channel withinner sidewall surfaces configured to receive the elongate rod, and alower portion defining a cavity communicating with the U-shaped channeland a receiver bottom opening, the shank positionable within thereceiver with the shank anchor portion extending through the bottomopening, the inner sidewall surfaces including a guide and advancementstructure formed therein, the receiver having an internaldownward-facing surface located between the guide and advancementstructure and the receiver bottom opening; and a pressure insert sizedand shaped to be disposed downwardly into a first position within thereceiver adjacent the receiver downward-facing surface, after the shankhas been positioned within the receiver, with the shank proximal captureportion outer spherical surface frictionally engageable with thepressure insert for directly receiving downward pressure from thepressure insert, the pressure insert having an upward-facing surfaceconfigured to engage the receiver downward-facing surface, wherein thepressure insert is rotatable with a tool about the receiver longitudinalaxis into a second position within the receiver, with the insertupward-facing surface entering into frictional engagement with thereceiver downward-facing surface, so as to apply downward pressure tothe shank proximal capture portion outer spherical surface by biasedoverlapping engagement therebetween so as to provide a frictionallyarticulatable relationship for the shank with respect to the receiverprior to the elongate rod being received within the receiver.
 13. Thebone anchor assembly of claim 12, wherein at least one of the insertupward-facing surface and the receiver downward-facing surface includesa sloped portion operable to provide a cam action that converts therotatory motion of the pressure insert into linear downward movement ofthe pressure insert.
 14. The bone anchor assembly of claim 13, whereinthe pressure insert continues to rotate toward the second position afterthe linear downward movement of the pressure insert is complete.
 15. Thebone anchor assembly of claim 12, wherein the receiver downward-facingsurface further comprises a discontinuous upper shoulder of a rigidrecess machined into the inner sidewall surfaces between the guide andadvancement structure and the receiver bottom opening.
 16. The boneanchor assembly of claim 15, wherein the insert upward-facing surfacefurther comprises at least one sloped portion operable to provide a camaction that converts the rotatory motion of the pressure insert intolinear downward movement of the pressure insert upon engagement with thediscontinuous upper shoulder of the recess.
 17. The bone anchor assemblyof claim 16, wherein the at least one sloped portion of the uppersurface further comprises a pair of sloped portions formed into theinsert upward-facing surface and operable to engage opposing portions ofthe discontinuous upper shoulder as the pressure insert is rotated aboutthe receiver longitudinal axis.
 18. The bone anchor assembly of claim17, wherein the insert upward-facing surface further includessubstantially horizontal portions adjacent the sloped portions andoperable to frictionally engage the discontinuous upper shoulder of therecess when the pressure insert is fully rotated to the second angularorientation.
 19. The bone anchor assembly of claim 12, wherein thepressure insert further includes a U-shaped cradle formed therein forengaging the elongate rod that aligns with the U-shaped channel of thereceiver when the pressure insert is fully rotated into the secondposition.
 20. The bone anchor assembly of claim 12, wherein the pressureinsert is rotated about 90 degrees around the receiver longitudinal axisfrom the first position to the second position.
 21. The bone anchorassembly of claim 12, wherein the pressure insert has a non-round shape,as viewed from above, with a width that is smaller than a lengththereof.
 22. The bone anchor assembly of claim 21, wherein the insertupward facing surface further comprises a U-shaped cradle extendingacross the width of the pressure insert.
 23. The bone anchor assembly ofclaim 12, wherein an upper surface of the pressure insert includes atleast one tool engagement structure complementary with an engagementportion of the tool.
 24. The bone anchor assembly of claim 23, whereinthe at least one tool engagement structure further comprises a pluralityof such tool engagement structures formed into the upper surface of thepressure insert.
 25. The bone anchor assembly of claim 12, furthercomprising a retainer sized and shaped for loading into the receivercavity to engage and hold the shank proximal capture portion within thereceiver while an outer surface of the retainer engages an interiorsurface of the receiver cavity to allow for pivoting motion between thereceiver and the shank to provide for a pivotal orientationtherebetween.
 26. A bone anchor assembly for securing an elongate rod toa bone, the bone anchor assembly comprising: a shank having a proximalportion with a partial spherical shape and an anchor portion extendingdistally from the proximal portion for fixation to the bone; a receiverhaving a first longitudinal axis, an upper portion defining a U-shapedchannel with inner sidewall surfaces configured to receive the elongaterod, and a lower portion defining a cavity communicating with theU-shaped channel and a receiver bottom opening with the shank anchorportion extending therethrough, the inner sidewall surfaces including aguide and advancement structure formed therein, the receiver having anon-threaded internal downward-facing surface radially spaced from thefirst longitudinal axis and located between the guide and advancementstructure and the receiver bottom opening; a closure configured to madewith the receiver guide and advancement structure; and a pressure inserthaving a second longitudinal axis and being sized and shaped to bedisposed downwardly into a first position within the receiver adjacentthe receiver downward-facing surface, the pressure insert having anon-threaded upward-facing surface radially spaced from the secondlongitudinal axis and configured to overlap with the receiverdownward-facing surface, wherein the pressure insert is rotatable with aremovable tool about the first and second longitudinal axes into asecond final rotational position within the receiver, with the insertupward-facing surface coming into an overlapping relationship with thereceiver downward-facing surface, so as to prevent the insert frommoving back up within the receiver, the insert being rotating into thesecond final position by direct engagement with the tool which isremoved from within the receiver prior to the closure being positionedtherein.
 27. The bone anchor assembly of claim 26, wherein the pressureinsert includes at least one tool engaging structure formed therein. 28.The bone anchor assembly of claim 26, wherein the receiverdownward-facing surface further comprises a discontinuous upper ledge ofa recess formed into the receiver between the guide and advancementstructure and the receiver bottom opening.
 29. The bone anchor assemblyof claim 26, wherein the pressure insert further includes a U-shapedcradle formed therein for engaging the elongate rod that aligns with theU-shaped channel of the receiver when the pressure insert is fullyrotated into the second final position.
 30. The bone anchor assembly ofclaim 26, wherein the pressure insert is rotated about 90 degrees aroundthe first and second longitudinal axes from the first position to thesecond final position.
 31. The bone anchor assembly of claim 26, whereina portion of the pressure insert has a non-round shape with a width thatis smaller than a length thereof.
 32. The bone anchor assembly of claim26, wherein an upper surface of the pressure insert includes at leastone off-axis tool engagement structure complementary with an engagementportion of the tool.
 33. The bone anchor assembly of claim 32, whereinthe at least one off-axis tool engagement structure further comprises aplurality of such tool engagement structures formed into the uppersurface of the pressure insert.
 34. The bone anchor assembly of claim26, further comprising a retainer sized and shaped for loading into thereceiver cavity to engage and hold the shank proximal capture portionwithin the receiver while an outer surface of the retainer engages aninterior surface of the receiver cavity to allow for pivoting motionbetween the receiver and the shank to provide for a pivotal orientationtherebetween
 35. A bone anchor assembly for securing an elongate rod toa bone via a closure, the bone anchor assembly comprising: a shankhaving a proximal portion and an anchor portion extending distally fromthe proximal portion for fixation to the bone; a receiver having alongitudinal axis, an upper portion defining a U-shaped channel withinner sidewall surfaces configured to receive the elongate rod, and alower portion defining a cavity communicating with the U-shaped channeland a receiver bottom opening for receiving the proximal portion of theshank therethrough, the inner sidewall surfaces including a guide andadvancement structure and opposed discontinuous non-threadeddownward-facing surfaces formed therein between the guide andadvancement structure and the receiver cavity; a retainer sized andshaped for loading into the receiver cavity to engage and hold the shankproximal portion in spaced relation with respect to the receiver whilean outer surface of the retainer engages an interior surface of thereceiver cavity to allow a pivotal motion between the receiver and theshank; and a pressure insert sized and shaped to be positioneddownwardly within the receiver into a first position, the pressureinsert having non-threaded upward-facing surfaces and being rotatablewith a tool into a second final position that locates the insertupward-facing surfaces under the receiver downward-facing surfaces toprevent the pressure insert from moving back up within the receiverprior to the elongate rod and the closure being placed within thereceiver channel.
 36. The bone anchor assembly of claim 35, wherein thepressure insert further comprises a central body havingradially-extending portions with the insert upward-facing surfaces thatare operable to rotate underneath the receiver downward-facing surfaceswhen the pressure insert is rotated about the receiver longitudinal axisinto the second final position.
 37. The bone anchor assembly of claim35, wherein the pressure insert is rotated about 90 degrees around thereceiver longitudinal axis from the first position to the second finalposition with the tool, and wherein the tool directly engages the insertand is removed from within the receiver prior to the elongate rod andthe closure being placed within the receiver channel.
 38. The boneanchor assembly of claim 35, wherein an upper surface of the pressureinsert includes at least one tool engagement structure complementarywith an engagement portion of the tool.